The present invention relates to new double metal cyanide (DMC) catalysts for the production of polyether polyols by polyaddition of alkylene oxides to starter compounds containing active hydrogen atoms.
Double metal cyanide (DMC) catalysts for the polyaddition of alkylene oxides to starter compounds containing active hydrogen atoms are known (see for example U.S. Pat. Nos. 3,404,109, 3,829,505, 3,941,849 and 5,158,922). The use of these DMC catalysts for the production of polyether polyols lead in particular to a reduction of the proportion of monofunctional polyethers with terminal double bonds, so-called monools, compared to the conventional production of polyether polyols by means of alkali metal catalysts such as alkali metal hydroxides. The polyether polyols that are thus obtained may be processed into high-grade polyurethanes (for example elastomers, foams, coatings). DMC catalysts are normally obtained by reacting an aqueous solution of a metal salt with an aqueous solution of a metal cyanide salt in the presence of an organic complex ligand, e.g. an ether. In a typical catalyst preparation aqueous solutions of zinc chloride (in excess) and potassium hexacyanocobaltate for example are mixed and then dimethoxyethane (glyme) is added to the resultant suspension. After filtration and washing the catalyst with aqueous glyme solution, an active catalyst of the general formula
Zn3[Co(CN)6]2xZnCl2yH2Ozglyme
is obtained (see e.g. EP-A 700 949).
From JP-A 4 145 123, U.S. Pat. No. 5,470,813, EP-A 700 949, EP-A 743 093, EP-A 761 708 and WO 97/40086 DMC catalysts are known, which by using tert.-butanol as organic complex ligand (alone or in combination with a polyether (EP-A 700 949, EP-A 761 708, WO 97/40086)) further reduce the proportion of monofunctional polyethers with terminal double bonds in the production of polyether polyols.
Furthermore, the induction time in the polyaddition reaction of alkylene oxides with corresponding starter compounds is reduced and the catalyst activity is raised by the use of these DMC catalysts.
The object of the present invention was to provide further improved DMC catalysts for the polyaddition of alkylene oxides to corresponding starter compounds that have an increased catalyst activity compared to the hitherto known types of catalyst. Due to the reduction of the alkoxylation times this leads to an improved economy of the production process for polyether polyols. Ideally, due to its increased activity the catalyst can then be used in such low concentrations (25 ppm or less) that the very complicated and costly separation of the catalyst from the product is no longer necessary and the product can be used directly for producing polyurethanes.
It has now surprisingly been found that DMC catalysts that contain an xcex1,xcex2-unsaturated carboxylic acid ester as complex ligand have a greatly increased activity in the production of polyether polyols.
The present invention accordingly provides a double metal cyanide (DMC) catalyst containing
a) one or more, preferably one double metal cyanide compound,
b) one or more, preferably one organic complex ligand different from c), and
c) one or more, preferably one xcex1,xcex2-unsaturated carboxylic acid ester.
The catalyst according to the invention may optionally contain d) water, preferably in an amount of 1 to 10 wt. %, and/or e) one or more water-soluble metal salts, preferably in an amount of 5 to 25 wt. %, of the formula (I) M(X)n from the production of the double metal cyanide compounds a). In formula (I) M is selected from the metals Zn(II), Fe(II), Ni(II), Mn(II), Co(II), Sn(II), Pb(II), Fe(III), Mo(IV), Mo(VI), Al(III), V(V), V(IV), Sr(II), W(IV), W(VI), Cu(II), and Cr(III).
Particularly preferred are Zn(II), Fe(II), Co(II) and Ni(II). X, which are identical or different, preferably identical, denote an anion preferably selected from the group comprising halides, hydroxides, sulfates, carbonates, cyanates, thiocyanates, isocyanates, isothiocyanates, carboxylates, oxalates or nitrates. The value of n is 1, 2 or 3.
The double metal cyanide compounds a) contained in the catalysts according to the invention are the reaction products of water-soluble metal salts and water-soluble metal cyanide salts.
Water-soluble metal salts suitable for the production of double metal cyanide compounds a) preferably have the general formula (I) M(X)n, wherein M is selected from the metals Zn(II), Fe(II), Ni(II), Mn(II), Co(II), Sn(II), Pb(II), Fe(III), Mo(IV), Mo(VI), Al(III), V(V), V(IV), Sr(II), W(IV), W(VI), Cu(II), and Cr(III). Particularly preferred are Zn(II), Fe(II), Co(II) and Ni(II). The anions X are identical or different, preferably identical, and are preferably selected from the group comprising halides, hydroxides, sulfates, carbonates, cyanates, thiocyanates, isocyanates, isothiocyanates, carboxylates, oxalates or nitrates. The value of n is 1, 2 or 3.
Examples of suitable water-soluble soluble metal salts are zinc chloride, zinc bromide, zinc acetate, zinc actetylacetonate, zinc benzoate, zinc nitrate, iron(II) sulfate, iron(II)bromide, iron(II)chloride, cobalt(II)chloride, cobalt(II)thiocyanate, nickel(II)chloride and nickel(II)nitrate. Mixtures of various water-soluble soluble metal salts may also be used.
Water-soluble soluble metal cyanide salts suitable for the production of double metal cyanide compounds a) preferably have the general formula (II) (Y)aMxe2x80x2(CN)b(A)c, wherein Mxe2x80x2 is selected from the metals Fe(II), Fe(III), Co(III), Co(II), Cr(II), Cr(III), Mn(II), Mn(III), Ir(II), Ni(II), Rh(III), Ru(II), V(IV) and V(V). Particularly preferably Mxe2x80x2 is selected from the metals Co(II), Co(III), Fe(II), Fe(III), Cr(III), Ir(III) and Ni(II). The water-soluble soluble metal cyanide salt may contain one or more of these metals. The cations Y are identical or different, preferably identical, and are selected from the group comprising alkali metal ions and alkaline earth metal ions. The anions A are identical or different, preferably identical, and are selected from the group comprising halides, hydroxides, sulfates, carbonates, cyanates, thiocyanates, isocyanates, isothiocyanates, carboxylates, oxalates or nitrates a as well as b and c are integers, the values for a, b and c being chosen so as to ensure the electroneutrality of the metal cyanide salt; a is preferably 1, 2, 3 or 4; b is preferably 4, 5 or 6; c preferably has the value 0. Examples of suitable water-soluble metal cyanide salts are potassium hexacyanocobaltate(III), potassium hexacyanoferrate(II), potassium hexacyanoferrate(III), calcium hexacyanocobaltate(III) and lithium hexacyanocobaltate(III).
Preferred double metal cyanide compounds a) that are contained in the catalysts according to the invention are compounds of the general formula (III)
Mx[Mxe2x80x2x,(CN)y]z,
wherein
M is defined as in formula (I) and
Mxe2x80x2 is defined as in formula (II), and
x, xxe2x80x2, y and z are integers and are selected so as to ensure the electroneutrality of the double metal cyanide compound.
Preferably
x=3, xxe2x80x2=1, y=6 and z=2,
M=Zn (II), Fe (II), Co (H) or Ni (II) and
Mxe2x80x2=Co (III), Fe (III), Cr (III) or Ir (III).
Examples of suitable double metal cyanide compounds a) are zinc hexacyanocobaltate(III), zinc hexacyanoiridate(III), zinc hexacyanoferrate(III) and cobalt(II)hexacyanocobaltate(III). Further examples of suitable double metal cyanide compounds may be found for example in U.S. Pat. No. 5,158,922. It is particularly preferred to use zinc hexacyanocobaltate(III).
The organic complex ligands b) contained in the DMC catalysts according to the invention are in principle known and are described in detail in the prior art (for example in U.S. Pat. Nos. 5,158,922, 3,404,109, 3,829,505, 3,941,849, EP-A 700 949, EP-A 761 708, JP-A 4 145 123, U.S. Pat. No. 5,470,813, EP-A 743 093, and WO 97/40086). Preferred organic complex ligands are water-soluble organic compounds with heteroatoms such as oxygen, nitrogen, phosphorus or sulfur, that can form complexes with the double metal cyanide compound a). Suitable organic complex ligands are for example alcohols, aldehydes, ketones, ethers, esters, amides, ureas, nitrites, sulfides and mixtures thereof. Preferred organic complex ligands are water-soluble aliphatic alcohols such as ethanol, isopropanol, n-butanol, iso-butanol, sec.-butanol and tert.-butanol. Tert-butanol is particularly preferred.
The organic complex ligand is added either during the catalyst preparation or immediately after the precipitation of the double metal cyanide compound a). The organic complex ligand is normally used in excess.
The DMC catalysts according to the invention contain the double metal cyanide compounds a) in amounts of 20 to 90 wt. %, preferably 25 to 80 wt. %, referred to the amount of finished catalyst, and the organic complex ligands b) in amounts of 0.5 to 30 wt. %, preferably 1 to 25 wt. %, referred to the amount of the finished catalyst. The DMC catalysts according to the invention normally contain 1 to 80 wt. %, preferably 1 to 40 wt. %, referred to the amount of the finished catalyst, of xcex1,xcex2-unsaturated carboxylic acid esters c).
Suitable xcex1,xcex2-unsaturated carboxylic acid esters c) for the production of the catalysts according to the invention are for example mono-, di-, tri- or polyesters of acrylic acid and alkyl-, alkoxy-, alkoxycarbonyl- and alkoxycarbonylalkylacrylic acids with alcohols containing 1 to 30 C atoms or polyether polyols.
Suitable as alcohol component are monohydric, dihydric, trihydric or polyhydric aryl, aralkyl, alkoxyalkyl and alkyl alcohols with 1 to 30 C atoms, preferably 1 to 24 C atoms, particularly preferably 1 to 20 C atoms; preferred are aralkyl, alkoxyalkyl and alkyl alcohols, alkoxyalkyl and alkyl alcohols being particularly preferred.
Also suitable as alcohol component are polyalkylene glycols and polyalkylene glycol ethers, preferably polypropylene glycols and polyethylene glycols or their ethers with molecular weights of 200 to 10000, preferably 300 to 9000, particularly preferably 400 to 8000.
Suitable as xcex1,xcex2-unsaturated carboxylic acids are acrylic acid and alkyl-, alkoxy- and alkoxycarbonylalkylacrylic acids with 1 to 20 C atoms, such as 2-methylacrylic acid (methacrylic acid), 3-methylacrylic acid (crotonic acid), trans-2,3-dimethylacrylic acid (tiglic acid), 3,3-dimethylacrylic acid (seneciocic acid) or 3-methoxyacrylic acid; preferred are acrylic acid, 2-methylacrylic acid, 3-methylacrylic acid and 3-methoxyacrylic acid; and particularly preferred are acrylic acid and 2-methylacrylic acid.
The xcex1,xcex2-unsaturated carboxylic acid esters used for the production of the catalysts according to the invention are as a rule obtained by esterification of mono-, di-, tri-, tetra- or polyhydroxy compounds with 1 to 30 C atoms, such as methanol, ethanol, ethanediol (ethylene glycol), 1-propanol, 2-propanol, 1,2-propanediol, 1,3-propanediol, 1,2,3-propanetriol(glycerol), butanol, 2-butanol, i-butanol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol, 1,4-butanediol, 1,2,3-butanetriol, 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, 1-decanol, 1-dodecanol, 1-tridecanol, 1-tetradecanol, 1-hexadecanol, 1-heptadecanol, 9-octadecanol, 1,1,1-tris(hydroxymethyl)propane, pentaerythritol, methoxymethanol, ethoxymethanol, propoxymethanol, butoxymethanol, 2-ethoxyethanol, 2-propoxyethanol, 2-butoxy-ethanol, hydroxyacetic acid methyl ester, hydroxyacetic acid ethyl ester, hydroxyacetic acid propyl ester, hydroxypropionic acid methyl ester, hydroxypropionic acid ethyl ester, hydroxypropionic acid propyl ester or polyether polyols such as polyethylene glycols and polypropylene glycols with the corresponding (xcex1,xcex2-unsaturated carboxylic acids, optionally in the presence of catalysts.
Preferred are mono-, di- and triesters of acrylic acid and methacrylic acid with ethanediol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,2,3-propanetriol(glycerol), 1,1,1-tris-(hydroxymethyl)propane, 1,1,1-tris-(hydroxymethyl)propane-ethoxylates, 1,1,1-tris-(hydroxymethyl)propane-propoxylates, polyethylene glycols and polypropylene glycols.
Particularly preferred xcex1,xcex2-unsaturated carboxylic acid esters are polyethylene glycol acrylic acid esters, polyethylene glycol diacrylic acid esters, polyethylene glycol methacrylic acid esters, polyethylene glycol dimethacrylic acid esters, polypropylene glycol acrylic acid esters, polypropylene glycol diacrylic acid esters, polypropylene glycol methacrylic acid esters, polypropylene glycol dimethacrylic acid esters, 1,2,3-propanetriol diacrylic acid esters, 1,2,3-propanetriol dimethacrylic acid esters, 1,2,3-propanetriol triacrylic acid esters, 1,2,3-propanetriol-1,3-(2-hydroxypropoxylate) diacrylic acid esters, 1,2,3-propanetriol-propoxylate triacrylic acid esters, 1,4-butanediol acrylic acid esters, 1,4-butanediol dimethacrylic acid esters, 1,6-hexanediol diacrylic acid esters, 2-hydroxypropyl methacrylic acid esters, 1,1,1-tris(hydroxymethyl)propane triacrylic acid esters, 1,1,1,-tris(hydroxymethyl)propane-ethoxylate triacrylic acid esters, 1,1,1-tris(hydroxymethyl)propane-ethoxylate trimethacrylic acid esters, 1,1,1-tris(hydroxymethyl)propane-propoxylate triacrylic acid esters or 1,1,1-tris(hydroxymethyl)propane-propoxylate trimethacrylic acid esters.
Methods for the production of xcex1,xcex2-unsaturated carboxylic acid esters are generally well known and are described in detail for example in xe2x80x9cKirk-Othmer: Encylcopedia of Chemical Technologyxe2x80x9d, Vol. 1, 4th Edition 1991, p. 291 et seq.; xe2x80x9cRxc3x6mpp: Lexikon Chemiexe2x80x9d, Vol. 1, 10th Edition, Stuttgart/New York 1996, p. 49. Vol, 4, 10th Edition, Stuttgart/New York 1998. p. 2629 et seq.; xe2x80x9cUllmanns Encyclopedia of Industrial Chemistryxe2x80x9d, Vol. A1, 5th Edition, 1995, p. 161 et seq.
Arbitrary mixtures of the aforementioned xcex1,xcex2-unsaturated carboxylic acid esters may also be used.
The analysis of the catalyst composition is normally performed by means of elementary analysis, thermogravimetry or extractive removal of the xcex1,xcex2-unsaturated carboxylic acid ester fraction followed by gravimetric determination.
The catalysts according to the invention may be crystalline, partially crystalline or amorphous. The analysis of the crystallinity is normally carried out by powder X-ray diffractometry.
Preferred are catalysts according to the invention containing
a) zinc hexacyanocobaltate (III),
b) tert.-butanol, and
c) an xcex1,xcex2-unsaturated carboxylic acid ester.
The production of the DMC catalysts according to the invention is normally carried out in aqueous solution by reacting xcex1) metal salts, in particular of the formula (I), with metal cyanide salts, in particular of the formula (II), xcex2) organic complex ligands b) that are different from the xcex1,xcex2-unsaturated carboxylic acid esters, and xcex3) xcex1,xcex2-unsaturated carboxylic acid esters.
Preferably first of all the aqueous solutions of the metal salt (e.g. zinc chloride, used in stoichiometric excess (at least 50 mole % referred to the metal cyanide salt)) and of the metal cyanide salt (e.g. potassium hexacyanocobaltate) are reacted in the presence of the organic complex ligand b) (e.g. tert.-butanol), a suspension being formed that contains the double metal cyanide compound a) (e.g. zinc hexacyanocobaltate), water d), excess metal salt e), and the organic complex ligand b).
The organic complex ligand b) may be present in the aqueous solution of the metal salt and/or of the metal cyanide salt, or it may be added directly to the suspension obtained after precipitation of the double metal cyanide compound a). It has proved advantageous to mix the aqueous solutions and the organic complex ligand b) while stirring vigorously. The suspension that is formed is then normally treated with the xcex1,xcex2-unsaturated carboxylic acid ester c). The xcex1,xcex2-unsaturated carboxylic acid ester c) is preferably used in a mixture with water and organic complex ligand b).
The catalyst is then removed from the suspension by known techniques such as centrifugation or filtration. In a preferred variant the separated catalyst is then washed with an aqueous solution of the organic complex ligand b) (e.g. by re-suspension followed by renewed separation by filtration or centrifugation). In this way for example water-soluble byproducts such as potassium chloride may be removed from the catalyst according to the invention.
Preferably the amount of organic complex ligand b) in the aqueous wash solution is between 40 and 80 wt. % referred to the total solution. Furthermore, it is advantageous to add to the aqueous wash solution some xcex1,xcex2-unsaturated carboxylic acid ester, preferably in an amount of between 0.5 and 5 wt. % referred to the total solution.
It is furthermore advantageous to wash the catalyst more than once. For this purpose the first wash procedure for example may be repeated. It is preferred however to use non-aqueous solutions for further wash procedures, e.g. a mixture of organic complex ligand and the xcex1,xcex2-unsaturated carboxylic acid ester.
The washed catalyst is then, optionally after it has been ground, dried at temperatures of in general 20xc2x0-100xc2x0 C. and at pressures of in general 0.1 mbar to normal pressure (1013 mbar).
The present invention also provides for the use of the DMC catalysts according to the invention in a process for the production of polyether polyols by polyaddition of alkylene oxides to starter compounds containing active hydrogen atoms.
As alkylene oxides there are preferably used ethylene oxide, propylene oxide, butylene oxide as well as their mixtures. The build-up of the polyether chains by alkoxylation may be carried out for example using only one monomeric epoxide, or may also be effected in a statistical or blockwise distribution with 2 or 3 different monomeric epoxides. Further details may be found in xe2x80x9cUllmanns Encyclopxc3xa4die der industriellen Chemiexe2x80x9d. Vol. A21. 1992. p. 670 et seq.
As starter compounds containing active hydrogen atoms there are preferably used compounds with molecular weights (number average) of 18 to 2,000 and containing 1 to 8 hydroxyl groups. The following may be mentioned by way of example: ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,4-butanediol, hexamethylene glycol, bisphenol A, trimethylolpropane, glycerol, pentaerythritol, sorbitol, raw sugar, degraded starch or water.
Preferably such starter compounds containing active hydrogen atoms are used that have been produced for example by conventional alkali catalysis from the aforementioned low molecular weight starter compound and that form oligomeric alkoxylation products faith molecular weights (number average molecular weight) of 200 to 2000.
The polyaddition of alkylene oxides to starter compounds containing active hydrogen atoms that is catalysed by the catalysts according to the invention is generally carried out at temperatures of 20xc2x0 to 200xc2x0 C., preferably in the range from 40xc2x0 to 180xc2x0 C. particularly preferably at temperatures of 50xc2x0 to 150xc2x0 C. The reaction may be carried out at total pressures of 0.001 to 20 bar. The polyaddition may be carried out in bulk or in an inert organic solvent such as toluene and/or THF. The amount of solvent is normally 10 to 30 wt. %, referred to the amount of polyether polyol to be produced.
The catalyst concentration is chosen so as to ensure a good control of the polyaddition reaction under the given reaction conditions. The catalyst concentration is generally in the range from 0.0005 wt. % to 1 wt. %, preferably in the range from 0.001 wt. % to 0.1 wt. %, particularly preferably in the range from 0.001 to 0.0025 wt. %, referred to the amount of polyether polyol to be produced.
The molecular weights (number average molecular weight) of the polyether polyols produced by the process according to the invention are in the range from 500 to 100,000 g/mole, preferably in the range from 1,000 to 50,000 gimole, particularly preferably in the range from 2,000 to 20,000 g/mole.
The polyaddition may be carried out continuously or batchwise, for example in a batch process or in a semi-batch process.
On account of their significantly improved activity, the catalysts according to the invention may be used in very low concentrations (25 ppm and less, referred to the amount of the polyether polyol to be produced). If the polyether polyols produced in the presence of the catalysts according to the invention are used for the production of polyurethanes (Kunststoffhandbuch, Vol. 7, Polyurethanes, 3rd Edition, 1993, pp. 25-32 and 57-67), removal of the catalyst from the polyether polyol can be omitted without adversely affecting the product qualities of the polyurethane that is obtained.